Hall effect sensors are used in a variety of systems to measure magnetic field. Hall effect sensors make use of the Hall effect, whereby a voltage is generated across a conductor or semiconductor due to Lorentz forces on moving charge carriers. This voltage, called the Hall voltage, can be measured to ascertain the strength of an applied magnetic field. The Hall voltage is inversely proportional to the density of charge carriers. Accordingly, Hall effect devices are often made of a semiconducting material with relatively lower charge carrier density than typical conductors.
Hall effect sensors can be either vertically or horizontally oriented in a semiconductor chip or die. Horizontal Hall effect devices, also called Hall plates, respond to a magnetic field component perpendicular to the main surface of the die in which they are formed. In contrast, vertical Hall effect devices respond to a magnetic field component parallel to the main surface of the die.
Four-contact and three-contact Hall effect devices are known. In a four-contact device, power (such as a supply current) is driven from a first contact to a second contact (usually positioned opposite the Hall effect device from the first contact along a primary axis). Third and fourth contacts are positioned to measure the Hall voltage generated by the current flow under the action of a magnetic field, and are likewise usually positioned opposite the Hall effect device from one another along a secondary axis. Third and fourth contacts are positioned such that in the absence of magnetic field they are at the same potential. This is often achieved by arranging primary and secondary axes perpendicular to one another. However, due to small inaccuracies and asymmetries in the device third and fourth contacts are usually not perfectly at the same potential at zero magnetic field. This gives a small voltage between these contacts which is called the offset error.
In a three-contact device, power (such as a supply current) is driven from a first contact to a second contact. The voltage at a third contact is a function of not only the power supplied, but also of any magnetic field incident upon the Hall effect device in a direction in which that device is sensitive. Three-contact devices can be arranged vertically (e.g., with a Hall effect region extending into the substrate in which the contacts are arranged) or horizontally (e.g., a Hall plate in which the Hall effect region is substantially coplanar with the three contacts).
The roles of the contacts (e.g., supply or signal contacts) in a three-contact vertical Hall effect device can be permuted to measure applied field in each of six distinct operating phases. This permutation is referred to as spinning Various offsets are produced during spinning operation. Within a given operating phase, at zero applied magnetic field, a signal voltage can be observed, referred to as “raw offset.” By spinning the Hall effect device and combining the resultant signal voltages in the complete spinning scheme, most of the raw offset can be corrected. The remainder is referred to as “residual offset.” “Electric offset” is the part of the offset that can be modeled by an equivalent resistor model of the Hall-effect device and switches. “Thermo-offset” refers to offset errors due to thermal effects such as Seebeck and Peltier effects occurring in the Hall effect device.
Generally speaking, spinning schemes for Hall effect devices attempt to produce high magnetic sensitivity, while reducing residual offset of the system. When using a spinning scheme, Hall effect devices are in general operated in an endless sequence of operating phases. This means that a spinning scheme comprising a certain number of operating phases is executed and the output signals of the Hall effect devices of these operating phases are combined; after executing the spinning scheme a first time it is repeated—perhaps intermittently and with scrambled or stochastic order—but endlessly as long as the circuit is powered on or operation is interrupted, when the circuit receives some command from external. So in a more general sense any repetitive sequence of finite operating phases, in which the Hall effect device is operated, is called a spinning scheme.